Process for the preparation of unsaturated carboxylic acids



United States Patent 3,369,043 PROCESS FOR THE PREPARATION OF UNSATURATED 'CARBOXYLIC ACIDS Irwin Schlossman, Whitestone, N.Y., assignor to Halcon International, Inc., a corporation of Delaware No Drawing. Continuation of application Ser. No. 272,536, Apr. 12, 1963. This application Apr. 28, 1967, Ser. No. 634,774

7 Claims. (Cl. 260530) ABSTRACT OF THE DISCLOSURE The present invention is directed to the production of unsaturated carboxylic acids from corresponding unsaturated olefins through oxidation with organic hydroperoxides in the presence of chromic acid as catalyst.

The subject application is a continuation of parent application Ser. No. 272,536 filed Apr. 12, 1963, now abandoned.

This invention relates to processes for the production of carboxylic acids from corresponding aldehydes and more particularly to the production of an unsaturated acid from a corresponding acrolein by oxidation of the latter with an organic hydroperoxide as the essential oxidizing agent, under the influence of a chromic acid catalyst.

The art has appreciated the desirability of being able to produce acrylic acids from the corresponding acroleins. However, because of undesirable side reactions, it has been necessary, generally, to resort to expensive indirect -methods for preparing such acids. A major problem is the tendency of the initial acrolein as well as the acrylic acid product to undergo polymerization to a co-polymeric product in an oxidizing environment making isolation of the monomeric acid or its esters substantially impossible. Another problem is the tendency of usual oxidation systems to attack points of nnsaturation instead of or in addition to the aldehyde group. Attempts have been made to avoid these difficulties by using a very dilute system or by using complicated procedures or by using involved catalyst systems all of which leave much to be desired. Accordingly, the art is confronted by the problem of providing processes for producing acrylic acids from corresponding acroleins in a convenient and economic manner.

The discoveries associated with the invention and relating to the solution of the above problems, and the objects achieved in accordance with the invention as set forth herein include the provision of:

a process for preparing an acrylic acid from the corresponding acrolein which comprises treating the acrolein with a combination of a chromic acid catalyst and an organic hydroperoxide as the essential oxidizing agent the amount of oxidizing agent being in the range of 0.1 to 2 mols per mol of the acrolein, and the amount of chromic acid is in the range of 0.003 to 0 .7 mol per mol of the acrolein;

such a process wherein the oxidizing agent is t-butylhydroperoxide and the temperature is in the range of about 50 to +150 C.;

such a process wherein the treatment is in a mutual solvent for the acid product and the acrolein;

such a process wherein the amount of the oxidizing agent is in the range of 0.5 to 1.0 mols per mole of the acrolein and the solvent is t-butanol;

such a process wherein the amount of chromic acid is in the range of 0.03 to 0.2 mol per mol of the acrolein and the temperature is in the range of 25 to 60 C.;

such a process wherein the acrolein is ordinary acrolein;

such a process wherein the acrolein is alpha-methacrolein;

3,369, 13 Patented Feb. 13, 1968 'ice such a process wherein the acrolein is alpha-chloracrolein;

such a process wherein the acrolein is alpha-ethylacrolein;

such a process wherein the acrolein is alpha-isobutylacrolein;

such a process wherein the acrolein is alpha-amylacrolein;

such a process wherein the concentration of the initial acrolein is in the range of 5 to 50% by weight;

such a process wherein the acrolein is methacrolein and its initial concentration is in the range of 5 to 15%;

and other objects which will be apparent as details or embodiments of the invention are set forth hereinafter.

In order to indicate still more fully the nature of the present invention, the following examples of typical procedures are set forth in which parts and percents mean parts and percents by weights, respectively, unless otherwise indicated, it being understood that these examples are presented as illustrative only and they are not intended to limit the scope of the invention.

Example 1 A mixture of t-butanol (41 grams), methacrolein (4.2 grams) chromic acid (added as solid CrO (1.0 gram), and t-butylhydroperoxide (5.3 grams), is mixed at room temperature and brought up to 40 C., and held there with agitation for three hours. The mixture analyzes 3.5% methacrylic acid, by gas chromatography. The methacrolein conversion is 48% and the selectivity of the reaction to methacrylic acid based on methacrolein is 81.5%.

Any convenient method of analysis may-be used.

The monomeric acrylic acid is separated by distillation, avoiding local overheating, and bubbling gaseous nitrogen through the mixture in order to inhibit polymerization.

Example 2 The procedure of Example 1 is repeated using a mixture of t-butanol (35 grams), methacrolein (10.5 grams), chromic acid (1.0 gram) and t-butyl-hydroperoxide (17.4 grams) at room temperature for three hours. The reaction mixture contains 11.3% methacrylic acid. The methacrolein conversion is 89% and the methacrylic acid selectivity based on reacted methacrolein is 72%.

The chromic acid may be prepared in situ from a sodium di-chromate and concentrated sulfuric acid, in known manner, if desired, and then used in the process with similar results. Equivalent forms of the chromic acid may be used, however prepared.

These are indeed surprising results, especially when one keeps in mind that the art has regarded chromic acid as a catalyst leading to attack on the olefinic double bond, and also in view of the high tendency of the aldehyde as well as of the acid to polymerize.

Example 3 The procedure of Example 2 is repeated using a mixture of methacrolein (10.5 grams), t-butanol (35 grams), chromic acid (1 gram), and cumene hydroperoxide (34 grams), at room temperature for 24 hours. The reaction mixture contains 2.7% methacrylic acid, the methacrolein conversion is 77% and the methacrylic acid selectivity based on reacted methacrolein is 21%.

Example 4 The procedure of Example 3 is repeated using ordinary acrolein in place of methacrolein. Acrylic acid is produced in comparable yields.

Example 5 The procedure of Example 3 is repeated with alphachloracrolein as the aldehyde, for producing alpha-chloracrylic acid, and similar results are obtained.

Example 6 The procedure of Example 3 is repeated with alphaethylacrolein as the aldehyde, for producing alpha-ethylacrylic acid, and similar results are obtained.

Example 7 The procedure of Example 3 is repeated with alphaisobutylacrolein as the aldehyde, for producing alphaisobutylacrylic acid, and similar results are obtained.

Example 8 The procedure of Example 3 is repeated with alphaamylacrolein as the aldehyde, for producing alpha-amylacrylic acid, and similar results are obtained.

Example 9 The procedure of Example 3 is repeated using cyclohexanone peroxide as the hydroperoxide and similar good results are obtained.

In the present invention, organic hydroperoxides are employed as oxidizing agents. T-butylhydroperoxide gives particularly outstanding results. Stable organic hydroperoxides generally are useful. Illustrative hydroperoxides can be represented generally by the formula ROOH where FR is an alkyl, alkenyl, alkynl, cycloalkyl, cycloalkenyl, aralkyl, aralkenyl, hydroxyalkyl, hydroxycycoalkyl, hydroxyaralkyl, and the like group having about 2 to 20 carbon atoms. Specific organic hydroperoxides are cumene hydroperoxide, cyclohexanone peroxide, cyclohexyl hydroperoxide, cyclohex-2-enyl hydroperoxide, and the like. Mixtures can be used.

The reaction is suitably carried out in the substantial absence of water. Relatively small amounts of water can be tolerated during the reaction but it is preferred to exclude water from the system during the major part of the reaction.

The process of the invention is particularly suitable for oxidizing unsaturated aldehydes for producing the corresponding monomeric acid, especially aldehydes and acids which have a strong tendency to undergo polymerization. Aldeh'ydes having up to 20 or more carbon atoms in the molecule may be used. The process may be applied to such compounds wherein the unsaturation is in any location in the molecule. The aldehydes may be substituted by hydroxy, ether, carboxylic acid, carboxylic acid ester, keto, nitro, and the like groups or halogen atoms.

The concentration of the aldehyde or acrolein in the reaction mixture may be in the range of to 50% by Weight preferably in the range of 5 to The reaction temperature may be from 50 to +150 C., desirably 0 to 100 C., and preferably in the range of room temperature or somewhat below up to about 60 C., the pressure may be atmospheric, or above or below, and the reaction time may be in the range of 10 minutes to 6 hours, and desirably 0.5 to 3 hours. For many runs, a one hour reaction time is suitable.

The amount of acid used as catalyst in the process can be varied widely although as a rule it is desirable to use at least 0.003 mol and more preferably 0.01 to 0.07 mol per mol of unsaturated aldehyde present. Amounts greater than about 0.7 mol seem to give no advantage over smaller amounts. The acid catalyst remains dissolved in the reaction mixture throughout the process and can be reused in the reaction after removal of the reaction products therefrom. A preferred range is 0.03 to 0.2 mol of the acid per mol of the aldehyde. The concentration of the hydroperoxide is in the range of 0.1 to 2 mols per mol of the acrolein, preferably 0.5 to 1.0.

The process is most advantageously carried out in the presence of a solvent.

A preferred solvent or diluent is t-butanol. However, other alcohols such as t-amyl alcohol, di-methyl propyl carbinol, methyl diethyl carbinol, dimethyl phenyl carbinol and the like may be used. Also, primary or secondary alcohols may be used, such as methanol, ethanol, nor i-propanol, ior nor s-butanol and the like pentanols or hexanols may be used. Also, ethers such as diethyl esters, ketones such as cyclohexanone may be used; or acids such as acetic acid, benzoic acid and the like may be used as Well as esters thereof such as methyl, ethyl, propyl, butyl, and the like. The lower aromatic hydrocarbons are suitable as well as the lower boiling chlorinated hydrocarbons including chlortoluene. Other saturated hydrocarbons or even unsaturated hydrocarbons may be used including purified butylenes, hexylenes, propylene trimers or tetramers, or butylene dimers or trimers using appropriate pressure to maintain the solvent in a liquid phase.

Where the unsaturated carboxylic acid produced is intended as an intermediate for further synthesis, one may use the solution of unsaturated acid in the solvent or diluent for this purpose directly without isolating the acid from the mixture. If the unsaturated carboxylic acid is to be esterified with a saturated alcohol, such an alcohol can be used as the solvent or diluent for the oxidation reaction and upon its completion the mixture can be heated to effect esterification and removal of the water formed. The eterification mixture can be distilled to separate the ester from the residue comprising impurities and catalyst. This residue contains the acid catalyst with any reaction by-products. The catalyst can be recovered and reused in subsequent oxidations.

The process may be carried out batchwise, or in an intermittent or continuous manner. As to the latter, the reaction may be carried out in an elongated reaction zone such as a tube or a tower or a plurality of reactors connected in series, and the hydroperoxide may be introduced at space points along the path of flow of the solution.

In view of the foregoing disclosures, variations and modifications thereof will be apparent to one skilled in the art, and it is intended to include within the invention all such variations and modifications except as do not come within the scope of the appended claims.

I claim:

1. A process for preparing an alpha-olefinically unsaturated carboxylic acid from an alpha-olefinically unsaturated aldehyde having up to 20 carbon atoms which comprises oxidizing the alpha-olefinically unsaturated aldehyde in the liquid phase with an organic hydroperoxide in the presence of a catalytic amount of chromic acid, the amount of hydroperoxide being in the range of 0.1 to 2 mols per mol of the alpha-olefinically unsaturated aldehyde, the amount of chromic acid being in the range of 0.003 to 0.7 mol per mol of the acrolein, and the oxidation temperature being in the range of about 50 to +150 C. r

2. The process of claim 1 wherein the hydroperoxide is t-butyl hydroperoxide.

3. The process of claim 1 wherein the oxidation is carried out in the presence of t-butanol solvent.

4. The process of claim 1 wherein the alpha-olefinically unsaturated aldehyde is propenal and acrylic acid is formed.

5. The process of claim 1 wherein the alpha-olefinically unsaturated aldehyde is methacrolein and the acid is methacrylic acid.

6. The process of preparing methacrylic acid which comprises oxidizing methacrolein in the liquid phase with t-butyl hydroperoxide as the essential oxidizing agent in the presence of a catalytic amount of chromic acid, the initial concentration of the methacrolein in the reaction mixture being 5 to 50% by weight, the amount of oxidizing agent being in the range of 0.1 to 2 mols per mol of methacrolein, the amount of chromic acid being in the range of 0.003 to 0.7 mol per mol of methacrolein and the temperature being in the range of about 0 to C.

7. The process of preparing acrylic acid which com prises oxidizing acrolein in the liquid phase with t-butyl hydroperoxide as the essential oxidizing agent in the presence of a catalytic amount of chromic acid, the initial concentration of the acrolein in the reaction mixture being 5 to 50% by weight, the amount of oxidizing agent being in the range 0.1 to 2 mols per mol of acrolein, the amount of chromic acid being in the range of 0.003 to 0.7 mol per mol of acrolein and the temperature being in the range of about 0 to 100 C.

References Cited UNITED STATES PATENTS 5/1956 Smith et a1 260530 

